Conventionally, for example, Japanese Patent Laying-Open Nos. 09-105419 (Patent Document 1) and 08-109918 (Patent Document 2) disclose a propeller shaft.
Patent Document 1 discloses a technique to apply a resin coating to a spline portion. As the spline portion is strongly affected by a surface of a counterpart sliding member, it is difficult to obtain desired friction characteristics with the resin coating. Namely, it is difficult to make a coefficient of static friction and a coefficient of dynamic friction substantially equal to each other.
Patent Document 2 discloses a technique to apply a plastic coating to a spline portion, however, desired friction characteristics cannot be obtained either.